A need has existed for a long time in the electronic packaging industry for a relatively simple, reliable and economical process for forming conductive patterns on non-planar and/or irregular surfaces. It has been desired to be able to form conductive patterns on both interior and exterior surfaces of non-planar and/or irregular bases. Screen printing has been suggested for applying conductive patterns to a non-planar but regular surface, such as the outer surface of a cylinder. A screen stencil was held up against the outer surface of the cylinder while the cylinder was rotated. Images then were formed on a part of the outer surface of the cylinder as it was rotated. A conductive pattern was formed from these images. However, screen printing techniques are difficult to apply to non-planar and/or irregular surfaces because it is difficult to keep the screen in contact with the non-planar and/or irregular surface.
Flexible printed circuits have been used in a limited number of applications to form conductive patterns on non-planar surfaces. These flexible printed circuits have limited flexibility. Also, the flexible printed circuit does not become as rigid as is needed in many applications.
Printed circuits have been formed on planar surfaces of materials such as nylon cloth, reinforced epoxy resins, which can be deformed into a limited number of shapes by the application of heat and pressure to the material. This deformation tends to cause the conductive patterns to rupture on the deformed outer surfaces and to wrinkle and delaminate from the base material on the inside of the deformed surfaces.
Today's printed circuit boards are essentially planar with conductive patterns on one or more parallel planes, the patterns being formed by the use of a glass or mylar type planar mask. Interconnection between the parallel planes is achieved via plated through holes. The planar surface of the board typically first is coated with a photosensitive material and then the planar mask, which contains the conductor pattern, is placed over and in contact with the board. The mask then is exposed to light or other radiation. This causes selected exposed portions of the photosensitive material to be altered in a variety of different known ways. The mask then is removed and the non-exposed portions of the photosensitive material are removed using a variety of different, known chemical etch processes. This leaves only the exposed portions of the photosensitive material that define the desired conductor pattern. Conductors are formed in the exposed or non-exposed portions of the surface of the board to form a conductor pattern. However, a planar mask cannot be effectively used to form conductive patterns on a non-planar and/or irregular surface of a printed circuit. The use of a planar mask on a non-planar surface results in some conductors which have greater or less than the desired widths and loss of control over the delineation of the desired conductive pattern.
It is desirable in many applications to be able to simultaneously form a plurality of conductors on an article having non-planar and/or irregular surfaces as well as planar surfaces.